Expanded graphite as superior anode for sodium-ion batteries

Graphite, as the most common anode for commercial Li-ion batteries, has been reported to have a very low capacity when used as a Na-ion battery anode. It is well known that electrochemical insertion of Na⁺ into graphite is significantly hindered by the insufficient interlayer spacing. Here we report expanded graphite as a Na-ion battery anode. Prepared through a process of oxidation and partial reduction on graphite, expanded graphite has an enlarged interlayer lattice distance of 4.3A yet retains an analogous long-range-ordered layered structure to graphite. In situ transmission electron microscopy has demonstrated that the Na-ion can be reversibly inserted into and extracted from expanded graphite. Galvanostatic studies show that expanded graphite can deliver a high reversible capacity of 284mAhg^-1 at a current density of 20mAg^-1, maintain a capacity of 184mAhg^-1 at 100mAg ^-1, and retain 73.92% of its capacity after 2,000 cycles.